The invention relates to a segmented polyetherester copolymer composition with improved thermooxidative stability. Thermooxidatively stabilized compositions are known, inter alia, from U.S. Pat. No. 4,205,158, where is described a copolyetherester with hard segments, derived from the alkylene diol butane diol and terephthalic acid or an ester thereof, and with soft segments, derived from an alkylene oxide glycol, predominantly consisting of an ethylene oxide-capped glycol of polypropylene oxide. The thermooxidative stability is obtained through addition of one or more N,Nxe2x80x2-alkylene bis(3,5-di-tert-butyl-4-hydroxy-hydrocinnamamides). In the above-mentioned publication use is made specifically of a combination of the hexamethylene-bis-(3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide) and the trimethylene-bis-(3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide). These compounds are commercially available under the tradenames Irganox(copyright) 1098 and 1019 of Ciba and are generally applied in the copolyetherester composition in a weight percentage of approximately 0.15/0.15. Such a combination is applied because especially the most active component, the Irganox(copyright) 1098, tends to bleed from the composition, which makes higher concentrations undesirable and in practice such higher concentrations also have a relatively small added stabilization effect on account of the bleeding. Commercially available copolyetherester compositions usually contain combinations of phenolic antioxidants on the basis of Irganox 1098(copyright). Other examples of thermooxidative stabilizers and combinations thereof are given in the book Thermoplastic Elastomers, 2nd ed., pp. 212-213, (1996), Carl Hanser Verlag, ISBN 3-446-175983-8. Since, in particular in automotive applications, various parts are subjected to ever higher thermal loads and absolutely no concessions can be made with respect to the life of parts produced from thermoplastic polyetherester copolymer, there is a need for further improvement of the resistance of segmented copolyetheresters. Examples of such parts include so-called inboard boots and convoluted tubes. Requirements to be met by those are that the flexibility does not drop below a certain value over a very long period, i.e. the life of the vehicle. In general the parts must be able to withstand at least 50% deformation without fracturing.
Due to these higher requirements, copolyetherester compositions whose performance was satisfactory in the past can no longer meet the current requirements of supplying a stable copolyetherester composition that can withstand the higher thermal load.
The aim of the invention is therefore to provide a segmented polyetherester copolymer composition with an improved stability at elevated temperature.
The inventors have succeeded in achieving this aim with a copolymer composition containing:
1) a segmented polyetherester copolymer derived from terephthalic acid or naphthalene dicarboxylic acid or an ester thereof, an alkylene diol, polypropylene oxide glycol that contains ethylene oxide end groups on the polypropylene oxide segments, and optionally a branching agent;
2) an effective amount of a stabilizer combination containing at least
(2a) at least one thermooxidative stabilizer chosen from the group of phenolic antioxidants and
(2b) at least one thermooxidative stabilizer chosen from the group of aromatic amines;
3) optionally other additives.
Component (1) is a segmented polyetherester copolymer the hard segments of which are built up of repeating alkylene terephthalate or alkylene naphthalate units, for instance butylene or propylene terephtalate, and the soft segments of which are derived from a polyether polyol built up of propylene oxide units, the last unit or units of the polyalkylene oxide of the chain being ethylene oxide units. The ratio between the numbers of propylene oxide and ethylene oxide units may vary within a wide range, for example between 20:1 and 1:6, preferably between 10:1 and 1:1. The ratio between the soft segment content and the hard segment content is not critical, either, for the aim of the invention and may vary within such a range that the Shore D hardness of the segmented polyetherester elastomer generally lies between 75 and 25. The hard segments may optionally also contain a minor number of units derived from another aromatic dicarboxylic acid, for example isophthalic acid, but the content thereof should be limited to ensure that, among other things, the crystallization behaviour of the copolyetherester is not adversely affected.
The molar weight of the segments may vary within a wide range, but preferably the molar weight, Mn, of the soft segments is chosen between 300 and 4000, more preferably between 500 and 3000, and most preferably between 750 and 2500.
Chain branching may have been effected with the customary branching agents. Examples are described in, inter alia, U.S. Pat. No. 4,205,158. Trimellitic acid or trimellitic anhydride and trimethylol propane are preferred. The content of branching agent, if present, is chosen such that a desirable melt viscosity is obtained. In general, the branching agent content will not be higher than 6.0 equivalents per 160 moles of terephthalic acid (+any other aromatic dicarboxylic acid that is present), preferably lower than 3.0, and most preferably lower than 1.5 equivalents per 100 moles of terephthalic acid.
The amount of (2) may vary within a wide range, depending on the requirements, for example 0.2-5 wt. %, and is determined mainly by the desired stability level. For a high stability a content of (2) of at least 0.5 wt. %, relative to the copolyetherester, is preferred, while maximum stability is obtained at a content of at least 1.5 wt. %, after which a further increase in the content has only a marginal effect. In general, the fraction of (2a) in (2) is smaller than the fraction of (2b). Particularly when (2a) has a tendency to bleed from the de composition, a relatively small fraction of (2a) is to be used.
The above does not imply that compositions with a content of (2) that is lower than 0.5 wt. % are not within the scope of protection of the present patent application. Besides the components (1) and (2) as already defined, the composition may contain yet other additives, for example UV stabilizers, thermooxidative stabilizers that are active via a different mechanism, for example an organic phosphorus compound or thio compound, colourants, carbon black, processing aids, for example release agents, fillers, etc.
The composition of the invention finds application in particular in objects that are subjected to frequent dimensional changes at elevated temperature. Examples include bellows used to seal universal joints in automobiles, bellows for shielding of spring systems, convoluted tubes, gaskets, etc.
Such objects made from the composition according to the invention form also part of the present invention.
The objects according to the invention can be obtained using the customary methods, for example injection moulding, compression moulding and blow moulding. Both the technology of injection moulding and that of extrusion blow moulding can be used with good results. The composition according to the invention is suitable in particular for blow moulding.
The choice of the molar weight and the degree of branching of (1) depend on the desired application and the processing technique required therefor. In general, the melt flow index (MFI) will be between 0.5 and 50 gr/10 min., with higher MFI values generally being required for injection moulding applications than for extrusion. For blow moulding a low MFI is necessary.
Examples of components (2a) and (2b), of which the activity in segmented polyether ester copolymers is described in the already cited book Thermoplastic Elastomers and the references therein, include:
(2a) phenolic antioxidants, more in particular hindered phenols:
2.6-di-tert-butyl-4-methylphenol known, inter alia, under the tradenames Ionol of Shell, Naugard(copyright) BHT of Uniroyal and Ultranox 226 of General Electrics;
2.6-di-tert-butyl-4-ethylphenol, Ethyl(copyright) 724 of Ethyl Corp;
2.2xe2x80x2-methylene-bis-(6-tert-butyl-4-methylphenol), the tradenames including Antioxidant BKF of Bayer, Oxichek 114 of Ferro and Ultranox 246 of General Electrics;
1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxy-phenyl) propionate, inter alia Anox(copyright) 20 of Great Lakes and Irganox(copyright) 1330 of Ciba-Geigy; N.Nxe2x80x2-hexamethylene-bis-(3,5-di-tert-butyl-4-hydroxy-hydro-cinnamamide) the Irganox(copyright) 1098 of Ciba-Geigy;
2.2xe2x80x2-oxamido-bis-ethyl-3-(3,5-di-tert-butyl-4-hydroxy-fenyl)-propionate), Naugard(copyright) XL1 of Uniroyal Chemical;
1,3,5-tris(3xe2x80x2,5xe2x80x2-di-t-butyl-4xe2x80x2-hydroxybenzyl)-s-triazine-2,4,6-(1H,3H,5H)trione, Irganox(copyright) 3114, Ciba-Geigy;
1,3,5-tri(4-t-butyl-2,6-dimethyl-3-hydroxy-benzyl)-isocyanurate, Cyanox(copyright) 1790 of Cytec; tetrakis [methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane, Irganox(copyright) 1010 of Ciba-Geigy;
2,2xe2x80x2-ethylidene bis (4,6-di-t-butylphenol), Isonox(copyright) 129 of Schenectady Chemicals;
2-propylene carboxylic acid, 2-idopentane 6[(3-isopentane-2-hydroxy-5-isopentane-phenyl)-ethyl]-4-methyl-phenyl-ester, Sumilizer(copyright) GS of Sumitomo;
p-cresol/dicyclopentadiene butylated reaction product, Ralox(copyright) LC of Raschig;
N,Nxe2x80x2-1,3-propane diylbis(3,5-di-t-butyl-4-hydroxyhydrocinnamamide);
(2b) aromatic amines
4.4xe2x80x2-di-cumyl-di-phenyl-amine, inter alia known under the tradename Naugard(copyright) 445 of Uniroyal Chemical;
N,Nxe2x80x2-di-phenyl-p-phenylene-di-amine, inter alia Permanex(copyright) DPPD of Vulnax;
4,4xe2x80x2-di-octyl-di-phenyl-amine, inter alia Vanox(copyright) 12 of R T Vanderbilt;
N,Nxe2x80x2-di-sec-butyl-p-phenylene-diamine, inter alia AO 22(copyright) of Dupont de Nemours or Topanol(copyright) M of ICI;
N,Nxe2x80x2-diphenylamine, Naugard(copyright) J of Uniroyal Chem;
poly-(2,2,4-trimethyl-1,2-dihydro-quinoline), Flectol(copyright) H of Monsanto.
The activity of both the phenolic antioxidants and the aromatic amines resides in their function of free radical scavenger. In view of this a more obvious solution would be, as also stated in the reference of Thermoplastic Elastomers, to choose a combination of stabilizers with different functions. An optimum result can for example be expected from the combination of a free radical scavenger, a hydroperoxide decomposer and optionally also a formaldehyde scavenger.
It is, therefore, very surprising that the combination of a phenolic antioxidant and an aromatic amine has such a very great effect on the thermooxidative stability of the segmented copolyetherester, this combination having this great effect only for the copolyetherester defined under component 1.